The invention relates to a projectile loom having a multiweft device, more particularly to the drive and weft changer of such device.
Through the agency of a yarn transfer element of the weft changer, such element being known conventionally as a giver or retractor, the weft yarn tip is pulled near the shears before the shed after picking and drawn back by means of a yarn tensioner; also, by means of the same yarn transfer element or, in the event of a yarn change, the different yarn transfer element the yarn for the next pick is transferred to the projectile by means of clamp openers. The changer body has guideways or slideways for the yarn transfer elements. When the same are in the drawn-back position the changer body can be pivoted through one or more steps to make a required change of color or weft yarn.
In the course of the development of projectile looms, during which productivity has increased continuously inter alia because of increasing loom speeds, no major improvements were made to the weft changers of multicolor looms for a long time (see e.g. DE-PS 942 979=T.175). In the end, however, the yarn changer proved to be a speed-determining component. More particularly in the case of cloths having, for example, four weft colors such that maximum pivoting movements of the changer were necessary because of the color sequence, loom speeds had to be reduced considerably as compared with the speeds of two-color or weft mixer looms. This led to the patterns of some fabrics being so modified that color changing involving extreme changing steps was abandoned in order to cut out extreme changer strokes and thus enable the looms to run faster. Of course the restricted choice of colors was not a satisfactory solution of the problem. Endeavours to solve the problem led to a reduction of the moment of inertia of the changer and of the mass of the yarn transfer elements to help reduce operating times.
The weft changer of known projectile looms is driven by the main shaft or the shedding motion by way of a control unit (see e.g. DE-PS 1 710 356=T.328). This kind of drive is elaborate and so there has for many years been a desire for a direct drive by means of a highly dynamic servo motor enabling the changer to be controlled directly. It is known to control warp tension by means of highly dynamic servo motors (EP-PA 0 350 447=T.757). A servo motor of this kind has, for example, electronic commutation and is brushless and has a low-weight rotor which has a low moment of inertia and which has high field strength permanent magnets. It is the object of the invention to provide a projectile loom with a multiweft device, more particularly for at least four colors, the weft changer being actuatable at a loom speed of more than 350 revolutions per minute by a direct drive--i.e., by a final control element acting directly on the changer.
The torques and outputs of conventional stepping or servo motors are too low to be of use instead of conventional weft changer drives. However, the development of highly dynamic servo motors has already advanced to such an extent that the problem addressed by the invention as hereinbefore set out can be solved.
As a result of the efforts to reduce the changeover times of weft yarn changers together with the concomitantly developed yarn transfer elements and changer bodies, highly dynamic servo motors such as are now available can be used for the direct drive of multiple weft devices in combination with the low-weight components of the weft yarn changer.